Abstract
Background
Currently, hip implant designs are evaluated experimentally using mechanical simulators or cadavers, and total hip arthroplasty (THA) postoperative outcomes are evaluated clinically using long-term follow-up. However, these evaluation techniques can be both costly and time-consuming. Fortunately, forward solution mathematical models can function as theoretical joint simulators, providing instant feedback to designers and surgeons alike. Recently, a validated forward solution model of the hip has been developed that can theoretically simulate new implant designs and surgical technique modifications under in vivo conditions.
Objective
The objective of this study was to expand the use of this hip model to function as an intraoperative virtual implant tool, thereby allowing surgeons to predict, compare, and optimize postoperative THA outcomes based on component placement, sizing choices, reaming and cutting locations, and surgical methods.
Methods
The math model simulates the quadriceps muscles, hamstring muscles, gluteus muscles, iliopsoas muscles, tensor fasciae latae, and an adductor muscle group, as well as the ischiofemoral, iliofemoral, and pubofemoral hip capsular ligaments. The model can simulate resecting, weakening, loosening, or tightening of soft tissues based on surgical techniques. Additionally, the model can analyze a variety of activities, both weight-bearing and non-, including swing and stance phase of gait, deep knee bend, and more. The model was previously validated using telemetric implants and fluoroscopic results from existing implant designs.
Results
First, the model tool has capabilities that will allow surgeons to pre- or intra-operatively experiment with various surgical alignments, component designs, sizes, and offsets, as well as reaming and cutting locations. The model tool will incorporate a built-in CT scan bone database which will assist in determining muscle and ligament attachment sites as well as bony landmarks. The model tool can be used to assist in the placement of both the femoral component (Figure 1) and the acetabular cup (Figure 2).
Moreover, once the surgeon has decided on the placements of the components, he or she can use the modelling capabilities of the tool to run virtual simulations based on the chosen parameters. The simulations will reveal force and motion predictions of the hip joint based on the current component positioning (Figure 3). The surgeon can then choose to modify the positions accordingly or proceed with the surgery.
Discussion
Being able to intraoperatively predict postoperative mechanics will improve the functional outcomes of total hip arthroplasty and reduce the frequency of postoperative complications.
